The basic role of protective clothing is to prevent hazardous toxic materials such as chemicals, microorganisms and the like from coming into contact with the living body; to protect from weather hazards; etc.
In principle, such results can be accomplished by making the clothing from a continuous barrier material which is impermeable to water, wind and/or any hazardous or undesirable substances present in the surrounding atmosphere. Impermeable protective clothing, as known to date, however, imposes intolerable restrictions on the natural process of heat dissipation from the human body, which normally occurs by sweat evaporation. The restriction on the thermal regulation of the human body by impermeable protective clothing induces development of thermal stress which may lead in extreme cases to thermal shock and death. Therefore impermeable protective clothing was found unsuitable for prolonged use under any condition, and in particular when the user is expected to perform intensive physical labour.
It is widely accepted in the art that in order to solve the thermal stress problem of protective clothing, adequate means for eliminating the sweat from the interior of the suit to the environment must be found.
Until now, this problem was addressed by using porous protective materials, which allow free flow of air and other gases through their pores and selectively removing or trapping the damaging components present in the surroundings. An example of an embodiment of this approach are the Gortex (trade mark) sport and rainwear which are made of microporous polytetra fluoro ethylene (PTFE), which allows relatively free passage of gases and water vapor but is not wetted by liquid water, thus providing very efficient water repelency combined with permeability to water vapors and air. Another example of this kind of protective clothing are the so-called "breathing" CBA (chemical, biological, atomic) protective suits, which are based on activated carbon impregnated porous textiles, felts or sponges, which are open to free flow of air. These "breathing" protective clothes allow elimination of the sweat through the pores of the textile while at the same time toxic compounds are adsorbed by the activated charcoal.
While this "breathing" air-permeable protective clothing makes allowance for and reduces the problem of heat dissipation by sweat evaporation, it has the inherent drawback of being permeable also to hazardous vapours, aerosols and particulate materials. Furthermore, the so-called "breathing" clothing are characterized by intrinsic bulkiness due to the fact that they are designed for carrying relatively large loads of adsorbent material required to provide protection against toxic chemicals during a reasonably sufficient period of time. It is also well recognized that the breathing materials also do not provide adequate solution to the physiological load and heat stress problems of the chemical protective garments, and they also may lead to incapacitation and thermal shock and even death under conditions of severe work loads, and high temperatures and humidity. In spite of these inherent short-comings, so far no better solutions have been found and the protective clothing made of "breathing" materials are widely used both for civil and military applications.
German patent specifications DE-A1-31 323 24 and DE-A1-32 009 42 disclose moisture permeable, waterproof airtight textile materials and their use for protective purposes and one of the disclosed embodiments is allegedly applicable for CBA protection. According to the disclosure in these two patent specifications foamed synthetic polymers such as foamed polyurethane, are used with the object of exercising a buffer effect by absorbing sweat as it develops and gradually releasing it to the atmosphere. Several features of the materials disclosed in these patents indicate, however, that they cannot provide simultaneously adequate heat stress relief and chemical protection.
One of the main problems inherent in the protective materials and garments disclosed in DE-A1-31 323 24 and DE-A1-32 009 42 concern their thermal conductivity. It can easily be shown that in order to allow adequate cooling of the body, protective clothing, in addition to being water permeable should also have an as high as possible thermal conductivity and to this end any void due to entrapped gas bubbles should be eliminated as far as possible from the structure of the protective material, having regard to the thermal insulating properties of such voids. The foamed synthetic polyurethane materials used in accordance with the above two German patent specifications have intrinsically a large number of voids and consequently do not allow for adequate body heat dissipation.
Furthermore, due to the accumulation of sweat in the foamed synthetic material in accordance with the teachings of the said two German patent specifications, there results a considerable added weight which contributes significantly to the wearer's discomfort.
The materials described in the above two German patent specifications are not satisfactory, even as far as moisture dissipation is concerned. Thus, the moisture permeability of the protective textiles according to DE-A1-31 323 24 is limited to values of up to 42 g/m.sup.2 /h which is considerably lower than the values of 250-500 g/m.sup.2 /h eliminated by the human body as sweat during periods of intensive activity.
Moreover, even a capability of eliminating sweat by permeation at a rate of 250-500 g/m.sup.2 /h or higher, dictated by metabolism, does in itself not necessarily provide the desired cooling effect to the human body. The vaporization heat absorbed during the evaporation process is taken from the immediate vicinity of the evaporation surface. Therefore the efficiency of the cooling effect of the human body depends on the distance of this evaporation surface from the body and on the thermal conductivity of the medium which separates this evaporation surface from the skin. When sweat evaporation occurs in the pores of the human skin itself, the cooling effect achieved is the most efficient possible. However, in the case of a protective garment, particularly if it is airtight even if water permeable, the sweat evaporation may essentially occur only on the external surface of the protective barrier, which is not necessarily in close contact with the skin. As a result, in such cases the cooling efficiency with regard to the human body will be considerably lower than the values expected from considering the amount of sweat eliminated by the body. This effect is aggravated when the protective barrier has a relatively low thermal conductivity in consequence of a porous or foamy structure. Thus, in experiments conducted preparatory to the present invention with known porous, "breathing" protective suits it was shown that even where, in consequence of permeability, the rate of moisture transport was of the order of 250-500 g/m.sup.2 /h as required by human metabolism, such suits caused inadequately high levels of heat stress in spite of their air permeability. This was true in particular in regard to suits which were based on polyurethane foams and it demonstrates the importance of thermal conductivity for the provision of adequate heat relief.
Summing up, the protective materials and garments disclosed in DE-A1-31 323 24 and DE-A1-32 009 42 have serious intrinsic deficiencies and the disclosure does not provide any evidence that adequate chemical protection and/or heat stress relief was or indeed can be achieved by the disclosed methods and materials.
There are known in the art various non-porous materials with yet a sufficiently high permeability to water to allow efficient thermal regulation of the body by natural sweat and heat elimination processes, examples being polymers such as polyvinyl alcohol, polyvinyl pyrrollidone, acrylamide polymers, polyurethanes, etc. It is also known to impart water permeability properties to common, water impermeable synthetic poly meric materials by grafting techniques. However, while the water permeability of known materials obtained in this way is occasionally sufficiently high to allow water transport rates comparable to the sweating rate of an average person performing intensive physical work, such permeability is as a rule accompanied by a permeability to toxic gases with the consequence that such materials are inadequate for protection against noxious and toxic chemicals in the form of vapors and aerosols.
It is the object of the present invention to overcome the deficiencies of the prior art and provide a non-porous protective material which has yet a sufficiently high water permeability and thermal conductivity to enable adequate heat and moisture dissipation and thereby to afford adequate cooling of the body during intensive labour and at the same time also effective protection against weather hazards and/or noxious and toxic chemicals in the form of vapours, aerosols and particulates.